In a known display apparatus, various display elements (e.g., alphabetic and numeric characters) may be displayed with any of a number of attributes. Thus, the characters may be highlighted, may be underlined, may be displayed in reverse video, may be concealed, or may be presented in blinking (i.e., on-and-off) form.
Where the commands for providing particular attributes to the characters are provided by a host computer, similar commands are also provided to negate the above described attributes. Thus, an underline may be removed from a character, a character may be caused to stop blinking, or may be presented in normal video, etc., upon provision to the display of a negating command for any of the above described attributes.
Similarly, line displays, as well as displays of lines of characters, may be provided with particular attributes. Particularly, lines of displayed characters may be displayed in double-width, double-size, or normal size. Finally, a screen attribute may be provided in which the foreground characters are displayed in one shade or color and in which the background is displayed in another shade or color. The shading or coloration of the characters and/or display background may be varied, and a particular arrangement may be selected in default situations.
In some display systems it is known to provide display commands in which the displayed characters are changed. Thus, in a touch control screen, for example, wherein a touch control panel is mounted on a display screen, various characters are displayed in particular regions of the screen providing the various touch controls, the displays associated with each touch control region may require variation for different applications. One or more of the regions may be changed while others may remain constant from application to application.
Further, various interactive or warning messages may be displayed on the screen. Such messages may be changed from moment to moment.
In an existing system a host computer conveys commands to a controller in the display for changing the characters displayed thereon. However, in such a system it is known that, together with a change in a displayed character the attributes thereof are changed, unless a specific command is provided either to retain the current attribute or to change the same. Accordingly, in such a system a change of display contents alone is made difficult since, in addition to providing the new characters for display the host computer must also provide to the display controller commands for setting the character attributes. Thus, updating characters within a particular field of the display requires communication of additional commands to identify provision of the same attributes that previously were present. Similarly, when a display is scrolled on a screen, each new line coming onto the screen must be accompanied by a command providing therefor the attributes, even though the attributes may not change from line to line.
There is thus a need to improve known display devices and to eliminate the necessity for provision of repetitive attribute commands. More specifically, there is a need for method or apparatus for permitting changes in contents of a display while maintaining constant the attributes of the display.